Chap. I. TWINING PLANTS. 17 



do not possess any such quality, for directly after 

 putting a stick to the Lophosjjermvm, I saw that it 

 behaved differently from a true twiner or any other 

 leaf-climber.* 



The belief that twiners have a natural tendency to 

 grow spirally, probably arose from their assuming a 

 spiral form when wound round a support, and from the 

 extremity, even whilst remaining free, sometimes 

 assuming this form. The free intemodes of vigor- 

 ously growing plants, when they cease to revolve, 

 become straight, and show no tendency to be spiral ; 

 but when a shoot has nearly ceased to grow, or when 

 the plant is unhealthy, the extremity does occasionally 

 become spiral. I have seen this in a remarkable 

 manner with the ends of the shoots of the Stauntonia and 

 of the allied AJcebia, which became wound up into a close 

 spire, just like a tendril ; and this was apt to occur after 

 some small, ill-formed leaves had perished. The ex- 

 planation, I believe, is, that in such cases the lower parts 

 of the terminal intemodes very gradually and suc- 

 cessively lose their power of movement, whilst the 

 portions just above move onwards and in their turn 

 become motionless ; and this ends in forming an 

 irregular spire. 



When a revolving shoot strikes a stick, it winds 

 roimd it rather more slowly than it revolves. For 

 instance, a shoot of the Ceropegia, revolved in 6 hrs.. 



t Dr. H. de Yries states (ibid. p. 322) that the stem of Cuscuta is 

 irritable like a tendrjl. 



